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This list compiles important numbers associated with the country or territory. They may be not so important for data users, but are essential for telephony. Even as a data user you still have to use some of them for top-ups or other SIM management purposes: * Country Calling Code * Mobile Country Code (MCC) * International Dialing Prefix (IDD) * Trunk Prefix Country Calling Code Country Calling Codes or country dial in codes are telephone dialing prefixes for the member countries or regions of the International Telecommunication Union (ITU) defined by ITU-T standards E.123 and E.164. The prefixes enable international direct dialing (IDD), and are also referred to as international subscriber dialing code (ISD). Country codes are a component of the international telephone numbering plan and are necessary to establish a call to another country. Country codes are dialed before the national telephone number. By convention, international phone numbers are represented by prefixing the country code with a plus sign (+'''), which also indicates to the subscriber that the local international call prefix must first be dialed. '''Mobile Country Code (MCC) A Mobile Country Code (MCC) is used in combination with a Mobile Network Code (MNC) (a combination known as an "MCC/MNC tuple") to uniquely identify a mobile network operator (carrier) using the GSM (including GSM-R), UMTS, and LTE public land mobile networks. Some but not all CDMA, iDEN, and satellite mobile networks are identified with an MCC/MNC tuple as well. It's based on ITU-T Recommendation E.212. International Dialing Prefix (IDD) An International call prefix also called dial out code or is a trunk prefix used to select an international telephone circuit for placing an international call. It's often referred to as IDD Prefix or International Access Code '''too and synonymous with '''exit code. The international dialing prefix must be dialed before the country calling code (see above) and the destination telephone number. The international prefix is part of the telephone numbering plan of a country for calls to another country. The ITU recommends the sequence 00 as a standard for an international prefix, and this has been implemented by many countries, but not all of them. When phone numbers are published for use abroad, they typically show a plus sign (+') prefix in place of any international call prefix to signify that the caller should use the prefix code appropriate for their country. Many phones allow the plus sign to be entered in their saved number lists, often by holding down the zero ('0) key (on most mobile phones). When making a call, the system then automatically converts the plus sign to the correct international prefix, depending on where the phone is being used, which enables callers to use the same stored number when calling from either their own country or any other. Trunk Prefix A trunk prefix is a digit sequence to be dialed before a phone number to initiate a phone call for the purpose of selecting an appropriate telecommunications circuit by which the call is to be routed. Making a domestic (national) telephone call usually requires the dialing of a single or two-digit national trunk prefix preceding any area codes and the destination subscriber number. In some countries, the trunk prefix is 0'''. In the North American Numbering Plan states, such as the U.S. and Canada, it is '''1. In some other countries, there is no trunk prefix. For international phone calls, the national trunk prefix is not dialed; instead, the international dialing prefix (see above) is typically required. To avoid a mix-up with all these prefixes whether dialled locally, nationally or internationally, the ITU recommends the international way of writing phone numbers. These should be the preferred way of storing them in your phone, because this sequence works from almost everywhere: + Graphic